Bengara (red oxide: Fe₂O₃) and shu (vermillion: HgS) are two typical pigments which had been used in red-colored urushi objects; of the two, bengara especially, is found in objects made in periods later than the Edo period. Ordinary bengara is a natural pigment made from hematite. However, it was found that through research of some old manuscripts, much synthetic bengara had been produced during the Edo period with different techniques, resulting in some with poor quality under mass production. This paper presents the general process used in making bengara during the Edo, consulting some old manuscripts and testamonies of some experienced workers who made synthetic bengara. It was found that workers of the Edo period used weathered roha (FeSO₄.7H₂O) as raw material, roasted it and then refined it in water.